This invention concerns the hygienic protection of container cans for food products and drinks, and in particular drink cans having in their upper end a tear-off opening through which the drink is consumed possibly by bringing the can directly to the mouth
The widespread practice of conserving drinks in cans has raised the general problem of safeguarding the health of the user. In this respect, after being filled, the cans are transported and stored without it in practice being possible to protect them from dust or other more dangerous contaminants, making the consumption of the liquid highly anti-hygienic whether the liquid is poured into a tumbler, or, much more serious, whether the user drinks it directly from the can.
The situation is further aggravated by the appearance of cans in which the opening tab is not pulled off, but instead bent down into the interior of the can, into direct contact with its contents.
There is therefore the need to protect the can upper end containing the opening tab from dust and other contaminants.
Method are known to protect the top of cylindrical objects having the same general shape of the cans:
FR-A-2 320 241 discloses a method and an Apparatus for covering a group of batteries according to which the batteries are covered by a plastic sheet which is moulded over the battery buds by the application of heat and pressure onto the material, realizing a cover for each single battery of the group.
The batteries may be arranged in a number of patterns, in single or double rows or in a circle. A groove in the inside of the cover allows air to escape from the cover.
This type of packing is not suitable for cans, because of the different configuration of their upper part that prevents the cover to adhere perfectly to the can top.
The problem to protect the top of cans from dust and other contaminants has been solved by the solution disclosed in the copending application PCT/EP97/03716.
Said solution comprises heating a film of thermoformable plastic material and positioning it on the upper part of the can, then making it adhere to the surface of said upper part by extracting the air contained between this surface and the film. Finally, the film portion adhering to the can upper part is separated from the rest of the film. During the described procedure, the film is heated to a suitable temperature such that the film is able to satisfy the conditions for thermoformability, after which, by rigidifying following cooling, it remains intimately adhering to the surface which it covers, and retains its shape.
A cap is obtained formed from a film portion which mates with and covers the upper part of the can, to be easily removed from the can and replaced thereon to cover the region comprising the can opening and the entire can upper part and upper edge contacted by the lips, so maintaining this under positively hygienic conditions.
Improvements are also known in which the covering means are formed for groups of at least two cans, to provide packs of two or more cans joined by a single support sheet, which simultaneously protects their lid from contamination.
The aforedefined state of the art is described in International Application PCT/EP97/03716 published as WO98/04459 in the name of the present applicant.
The method and apparatus described in said WO98/04459 are susceptible to further improvements concerning mainly the extraction of the air contained between the film protecting the upper part of the can and its lid.
In the known art, the vacuum required to extract the air is easier to obtain the smaller the air quantity to be extracted.
The object of this patent is therefore to considerably reduce the air quantity to be extracted, and possibly eliminate it completely with consequent plant simplification.
According to the invention, to achieve these objects a film of thermoformable plastic material is heated and positioned on the upper part of a can or group of cans, and is made to adhere over the maximum possible area to the surface of said upper part by a thrust action which acts on the top of the film to urge the film downwards.
According to the improvement, said thrust action can be due either to the action of a convex deformable elastic pad which is pressed onto the upper part of the can to cause the film to adhere starting from the can center, or to the dynamic action of a compressed air jet directed towards the center of the can lid. In both cases it is advisable for the thrust action to be aided by subjecting that part of the film resting on the lid to vacuum acting from below to also eliminate the very small residual air pockets which tend to form at the lid periphery, in proximity to the projecting rim, as a result of the attachment of the lid to the top of the container.
According to a particularly improved embodiment of the invention, it has been found possible to totally extract the air even if a vacuum is absent.
All the objects of the invention are attained by a machine having the characteristics defined in the claims.